Jonathan Clausen

Simulating deformable particle suspensions using a coupled lattice-Boltzmann and finite-element method

A novel method is developed to simulate suspensions of deformable particles by coupling the lattice-Boltzmann method (LBM) for the fluid phase to a linear finite-element analysis (FEA) describing particle deformation. The methodology addresses the need for an efficient method to simulate large numbers of three-dimensional and deformable particles at high volume fraction in order to capture suspension rheology, microstructure, and self-diffusion in a variety of applications. The robustness and accuracy of the LBM-FEA method is demonstrated by simulating an inflating thin-walled sphere, a deformable spherical capsule in shear flow, a settling sphere in a confined channel, two approaching spheres, spheres in shear flow, and red blood cell deformation in flow chambers. Additionally, simulations of suspensions of hundreds of biconcave red blood cells at 40 % volume fraction produce continuum-scale physics and accurately predict suspension viscosity and the shear-thinning behaviour of blood. Simulations of fluid-filled spherical capsules which have red-blood-cell membrane properties also display deformation-induced shear-thinning behaviour at 40 % volume fraction, although the suspension viscosity is significantly lower than blood.

Parallel performance of a lattice-Boltzmann/finite element cellular blood flow solver on the IBM Blue Gene/P architecture

We discuss the parallel implementation and scaling results of a hybrid lattice-Boltzmann/finite element code for suspension flow simulations. This code allows the direct numerical simulation of cellular blood flow, fully resolving the two-phase nature of blood and the deformation of the suspended phase. A brief introduction to the numerical methods employed is given followed by an outline of the code structure. Scaling results obtained on Argonne National Laboratories IBM Blue Gene/P (BG/P) are presented. Details include performance characteristics on 512 to 65,536 processor cores.

Capsule dynamics and rheology in shear flow: Particle pressure and normal stress

In this paper, we examine the dynamics of an isolated capsule using a hybrid lattice-Boltzmann/finite-element method, with a focus on how the capsule dynamics affects the rheology of capsule suspensions. We study initially spherical capsules undergoing a “tank-treading” behavior in which the particle assumes an ellipsoidal shape at a steady orientation while the capsule’s membrane rotates. Of particular interest is the calculation of the particle pressure and a full characterization of the normal stresses. To date, results on capsule rheology only consider normal stress differences, which are insufficient to explain particle migration using the suspension balance model [P. R. Nott and J. F. Brady, “Pressure-driven suspension flow: Simulation and theory,” J. Fluid Mech. 275, 157 (1994)]. We also extend the results of R. Roscoe [“On the rheology of a suspension of viscoelastic spheres in a viscous liquid,” J. Fluid Mech. 28, 273 (1967)] using the solution for ellipsoidal particles of G. B. Jeffery [“The mot...

Numerical Modeling of an All Vanadium Redox Flow Battery

We develop a capability to simulate reduction-oxidation (redox) flow batteries in the Sierra Multi-Mechanics code base. Specifically, we focus on all-vanadium redox flow batteries; however, the capability is general in implementation and could be adopted to other chemistries. The electrochemical and porous flow models follow those developed in the recent publication by [28]. We review the model implemented in this work and its assumptions, and we show several verification cases including a binary electrolyte, and a battery half-cell. Then, we compare our model implementation with the experimental results shown in [28], with good agreement seen. Next, a sensitivity study is conducted for the major model parameters, which is beneficial in targeting specific features of the redox flow cell for improvement. Lastly, we simulate a three-dimensional version of the flow cell to determine the impact of plenum channels on the performance of the cell. Such channels are frequently seen in experimental designs where the current collector plates are borrowed from fuel cell designs. These designs use a serpentine channel etched into a solid collector plate.

Direct Numerical Simulation of Cellular Blood Flow Through a Model Arteriole Bifurcation

Blood is composed of a suspension of red blood cells (RBCs) suspended in plasma, and the presence of the RBCs substantially changes the flow characteristics and rheology of these suspensions. The viscosity of blood varies with the hematocrit (volume fraction of RBCs), which is a result not seen in Newtonian fluids. Additionally, RBCs are deformable, which can alter suspension dynamics. Understanding the physics in these flows requires accurately simulating the suspended phase to recover the microscale, and a subsequent analysis of the rheology to ascertain the continuum-level effects caused by the changes at the particle level. The direct numerical simulation of blood flow including RBC migration effects has the capability to resolve the Fahraeus effect of observing low hematocrit values near walls, the subsequent cell-depleted layer, and the presence of velocity profile blunting due to the distribution of RBCs.Copyright